At the present, the construction industry is using scanning LASER beams for a level and/or grade reference during many phases of the construction process. For example, when a lot is being prepared, it must be formed to the specified grade and slope before a foundation or road bed is laid. A laser beam, which travels in an ideal straight line, can be rotated about 360.degree. to form a plane that can have the proper slope. An optical detector can sense this laser beam and thus instruct a machine or operator that the land is being graded at the proper level and slope, or else that the blade of the grader must be adjusted in a certain manner.
This is presently accomplished using a set of detectors that is so arranged to detect when the laser beam is at the correct level, or whether it is too high or low. There are then three indications to the operator: one that indicates that the beam is too high, one that indicates that the beam is too low, and one that indicates the proper elevation.
Due to this limited feedback system, the operator does not know how far above or below the proper grade level the blade of the equipment is operating. In other words, the system is qualitative, no quantitative.
Also, to account for sloped grades, such as are used in parking lots and on roads for water drainage, the laser beam is tilted to accomplish this purpose. Then, in accordance with prior art techniques, two separate detectors are used, one on each end of the grader's blade. Therefore, once the laser and detectors are set, the grading machine can only operate in one direction. If the operator needs to turn around or grade in a different direction the laser and detectors must then be readjusted to accomplish this.
Inasmuch as the instant invention has application, for example, to an apparatus for automatically controlling a blade of earth working equipment such as a bulldozer, the following patents are being made of record:
U.S. Pat. No. 2,796,685 to Bensinger discloses a method for controlling the position of certain construction equipment by forming parallel radiation energy planes and automatically controlling the position of equipment in accordance with deviation from the energy planes.
U.S. Pat. No. 2,916,836 to Stewart discloses a method according to which a reference plane is formed by rotating a visible radiation source and detecting light by a light receiving device attached to a blade for controlling the blade by means of a motor or a hydraulic system using an electromagnetic valve.
U.S. Pat. No. 3,000,121 to Martin discloses a system for automatically controlling the blade of construction equipment in a vertical direction in which a reference plane is formed by a light beam and a light receiver is provided for detecting whether the center of the light receiver coincides with the center of the reference light beam and emitting a signal of a different polarity depending upon whether the center of the reference light beam is above or below the center of the light receiver.
U.S. Pat. No. 3,887,012 to Scholl et al discloses a circuit for controlling an earth working equipment which, in a device having a certain relation with a plane formed by narrow rotating beam of radiant energy of a fixed wavelength, a receiver has at least three channels and a light receiving element cathodes a light beam incident from all directions within 180.degree. or 360.degree. thereby to control the earth working equipment so that the light receiving element catches the light beam at its center.
In the Scholl et al patent, the patentees indicate nine distinct areas in their detector housing, but they are not using the nine areas in a quantitative manner. The center area has no detector in it, therefore actually eight detector sections are used. Due to this type of construction, a loss of laser detection would, quite unfortunately, not be noticed.
The detectors are connected in such a manner that the Scholl et al invention would have a very limited useful range, and saturation from the sun would pose a problem. The circuitry employed is overly complicated, and, although the present state of the device is indicated to the operator, it unfortunately does not indicate where the grader's blade is in relation to the reference beam.
Scholl et al mention that the reason for converting the detector's signals into digital form was for enhanced reliability and noise immunity. Then they convert the signals back to an analog voltage to control the position of the hydraulic valve, which would potentially be subject to noise errors.
The Carson U.S. Pat. No. 4,200,787 relates to an apparatus for sensing the location of a received beam of light, and includes a plurality of optical fibers, each having a receiving end and a terminal end. The receiving ends of the fibers are arranged in a predetermined pattern over a light reception area, and with the terminal ends arranged to direct the light that is received to a plurality of phototransducers for detection of the light beam.
Carson's sensor head, which holds the receiving ends of the optical fibers, includes a transparent plastic cylinder disposed on his earth moving machine in a substantially vertical orientation.
The light reception area is divided into a number of separate regions and the fibers for each such region are grouped together into separate fiber bundles, which in turn transmit received light to a separate phototransducer. By this technique, receipt of the light beam by any single fiber in a given region is detected by a single phototransducer, thereby permitting a relatively small phototransducer to detect received light over a much larger area.
The Carson invention is stated to be particularly useful in a system for controlling the elevation of the cutting blade of an earth moving machine, and can be used in combination with a rotating laser beam transmitter operative in fixed relation to the ground.
The Nielsen et al U.S. Pat. No. 4,829,418 teaches a method and apparatus for controlling an excavator to position the cutting edge, during a cut, to a desired depth. That invention is used in conjunction with a laser plane generator that generates a laser plane and which repetitively calibrates the reference coordinate system of the excavator every time a digging stick passes through the laser plane. In that manner, the control will be frequently and repetitively calibrated as the excavator hauls bucket-loads of dirt out of the ditch and will thus compensate for frequent movement of the excavator frame without requiring time-consuming re-establishment of the frame location.
The Nielsen invention is noted to utilize a control technique for controlling the cutting edge in relationship to the angular relationship between the various members of the excavator, and is stated to provide a very accurate determination of the position of the cutting edge, and to be capable of digging to a non-level grade as well as to a level one.
According to Nielsen, his control has means for monitoring the angle of displacement of the excavator from a vertical plane and the various angles between the members of the excavator and means for determining the position of the bucket cutting edge from these angles. A laser receiver is mounted on the stick member and is passed through the laser plane every time the stick is brought out of or put into a trench. The control determines the position of the laser receiver with respect to the excavator frame at the precise moment that the receiver detects the laser beam. This information is used to determine the location of the excavator frame with respect to the laser beam. The position of the bucket cutting edge with respect to the laser plane can therefore be accurately determined and is compared to a desired cutting distance with respect to the laser plane to operate the means that actuates the cutting edge.
Unfortunately, the Nielsen device is extremely complicated and expensive. The cost of such a device is beyond the reach of smaller excavating contractors, whereas our invention is easy to use and readily affordable.
It was to overcome the substantial disadvantages of these highly complex prior art arrangements that the present invention was evolved.